1. Field of the Invention
The subject invention relates to an air conditioning compressor assembly for a vehicle. More specifically, the subject invention relates to a method of manufacturing and attaching the front head member for the air conditioning compressor assembly.
2. Description of the Related Art
An Air conditioning compressor assembly for a vehicle comprises a housing that is typically constructed from a plurality of members. The compressor housing must maintain a gas tight seal against leakage. The compressor housing is closed on one end by a front head member. The front head member includes a bore through which a fastener (screw) passes therethrough for attaching the front head member to the compressor housing. It is common within the industry to refer to the fastener as a bolt. It should be understood that reference to the fastener includes like references to a screw, bolt, or the like. The compressor housing includes a closed or “blind” threaded aperture for receiving a threaded end of the fastener. The threaded aperture is not required to maintain a pressure tight seal as it is not exposed to the exterior of the compressor assembly.
The fastener includes a head portion with a shank portion extending axially therefrom. The head portion of the fastener covers an exterior sealing surface concentric with the bore. A pressure tight seal must be maintained between the fastener and the front head member sealing surface for preventing the leakage of a pressurized gas from the compressor assembly.
The compressor housing and the front head member are typically made of an aluminum alloy for weight reduction and ease of manufacture. The fastener is typically made of steel. The front head member bore has a diameter slightly greater than the diameter of the shank of the fastener. The difference in diameters provides a radial clearance therebetween to allow for easier insertion of the fastener through the bore.
The sealing surface is disposed on an exterior surface of the front head member and is concentric with the bore. The sealing surface is machined down into the outer surface of the front head member to assure a suitable flat surface for the fastener to seal against.
Traditionally, a sealing washer was used to form the seal between the fastener and the sealing surface. Recently, however, the fastener has been provided with a sealing pad disposed on a bottom surface of the head portion of the fastener for maintaining the pressure tight seal without the use of the sealing washer. The head portion of the fastener is therefore in direct sealing engagement with the machined sealing surface of the front head member.
It has been the common practice to cast the front head member of the compressor housing from an aluminum alloy using traditional die casting techniques. The bore and the sealing surface are either machined in separate and costly operations, or machined with a costly compound tool operation.